City of Punta Gorda Adaptation Plan Southwest Florida Regional ...

In addition to the

In addition to the effects of inundation represented by the simple geometric model described above, second-order effects occur due to changes in the spatial relationships among the coastal elements. In particular, the model computes exposure to wave action: if the fetch (the distance across which wind-driven waves can be formed) is greater than nine km, the model assumes moderate erosion. If a cell is exposed to open ocean, severe erosion of wetlands is assumed. Beach erosion is modeled using a relationship reported by Bruun (1962) whereby recession is 100 times the change in sea level. Wetlands on the lee side of coastal barriers are subject to conversion due to overwash as erosion of backshore and dune areas occurs and as other lowlands are drowned. Erosion of dry lands is ignored; in the absence of site-specific information, this could underestimate the availability of sediment to replenish wetlands where accelerated bluff erosion could be expected to occur. Coastal swamps and fresh marshes migrate onto adjacent uplands as a response of the water table to rising sea level close to the coast; this could be modified to take advantage of more site-specific predictions of water table elevations. The model was run given the minimum, mean, and maximum estimates of each of the SRES (Special Report on Emissions Scenarios). A brief description of each of these scenarios can be found in the SLAMM 4.1 technical documentation (Glick 2006); more extensive descriptions are in the Intergovernmental Panel on Climate Change report (IPCC 2001a). For simplicity, this report will focus on the A1 scenario in which the future world includes very rapid economic growth, global population that peaks in midcentury and declines thereafter, and the rapid introduction of new and more efficient technologies. In particular, the A1B scenario assumes that energy sources will be balanced across all sources (fossil, nuclear, solar, etc.). According to the model, significant overwash is predicted for the barrier islands around Charlotte Harbor resulting in major upland loss. Saturation and inundation will also negatively affect uplands that are predicted to decrease by 35 to 55% depending on whether the mean or maximum scenario is run. Existing tidal flats are also predicted to be all but eliminated by sea level rise. Mangroves are predicted thrive under these scenarios increasing by 75% to 119% provided the sea level rise is gradual. AdaptationPlan Page 82